THelper did the heavy lifting, but I did some additional digging and found some more info. The official UN closing press release from the climate action summit includes this paragraph:
65 countries and major sub-national economies such as California committed to cut greenhouse gas emissions to net zero by 2050, while 70 countries announced they will either boost their national action plans by 2020 or have started the process of doing so.
So it seems there are two different lists. There's a link later in the document to a list of the initiatives with those who have made commitments.
"70 countries announced they will [...] boost their national action plans by 2020"
This refers to the initiative: "Climate Ambition Alliance: Enhanced National Climate Plans":
[...] this group brings together the countries that are responding to the urgent need to reduce emissions in the next decade by signaling their intention to work towards enhancing the ambition of their [Nationally Determined Contributions] by 2020.
The link includes the list of 70 countries.
"65 countries and major sub-national economies [...] committed to cut GHG emissions to net zero by 2050"
This refers to the "Climate Ambition Alliance: Net Zero 2050":
[T]his group brings together countries, businesses, investors, cities and regions who are working towards achieving net-zero CO2 emissions by 2050. Members of this alliance are demonstrating genuine leadership either by having developed plans to achieve net zero CO2 emissions by 2050; by having identified this target as a long-term goal; or by advancing consultations on a long-term strategy for climate-neutrality in line with the Paris Agreement. Initiatives included are: ‘Carbon Neutrality Coalition’, ‘Under2 Coalition’, ‘Deadline 2020’, ‘Business Ambition for 1.5˚C - Our Only Future’ and the ‘UN-Convened Net Zero Asset Owner Alliance’. In addition to the countries listed as participants below, the European Union is also part of this initiative.
The link includes the list of participants, including:
- 102 cities
- 10 regions (such as U.S. and Australian states)
- 87 companies
- 15 investors
- 65 countries
The confusion comes from the fact that the press release (which was distributed to the New York Times and the Straits Times) should have read this way:
65 countries and 10 major sub-national economies such as California committed to cut greenhouse gas emissions to net zero by 2050 ...